They were the ones who needed help.A Brooklyn couple who hosted a self-help radio show committed suicide by suffocating themselves with helium and plastic bags — leaving behind tragic suicide notes detailing a battle with bipolar disorder, police sources and witnesses said.Psychotherapist Lynne Rosen, 46, and her motivational-speaker husband John Littig, 48 — who appeared on WBAI-FM’s “The Pursuit of Happiness”— rigged tubes to a helium tank then tied plastic bags around their heads at their Park Slope home, the sources said.“I can’t take it anymore, my wife is so sick. She’s in too much pain. Please bury us together,” Littig wrote, according to a building manager who discovered the couple dead.Rosen’s note proclaimed she loved her husband — but couldn’t go on living.Building manager Hasan Boztepe, 51, found the couple on a living-room couch Monday morning — after neighbors complained about a foul smell coming from the home on President Street and Eighth Avenue.Boztepe first knocked, then broke down the door.“It was very, very bad,” Boztepe said. “They were sitting on the couch holding hands together. The bodies were black and very swollen.“I’ve never seen anything like this before. It’s crazy,” he said.Next to them were the handwritten suicide notes.Cops later discovered Rosen’s medication for bipolar disorder and anxiety, police sources said.On the radio show, the couple offered callers advice on how to lead happier lives, encouraging them to think positively and trust their intuition.But things were dark at home.On their brownstone-lined block, the two had a reputation for being reclusive, and Rosen sometimes appeared unhealthy, neighbors said.“John was a very nice person. Lynne kept to herself . . . She was always putting on a lot of weight and taking it off,” one neighbor said.Littig sometimes looked too thin and often walked outside in his slippers, said Terrence Thompson, 52, who does work on a nearby apartment.The double-suicide stunned and saddened residents on the quiet street.“Everyone is shocked . . . Everyone is wondering why,” said one neighbor.“That’s really distressing that they were life coaches, handing out advice to people.”Littig, who attended Long Island University, was also a drummer and a singer in the band Jadex. He performed at Webster Hall last winter.